The present invention relates to a method and apparatus for eliminating zebra mussel colonization in intake pipes for power plants, or the like, which makes use of alternate intake pipes.
In recent years, infestation of fresh water pipe inlets by zebra mussels has presented a serious problem to power plants, manufacturing facilities, refineries and municipal water suppliers which draw water from the Great Lakes. Zebra mussels have been spreading throughout the Great Lakes since they were first discovered in 1988 in Lake Saint Clair, and are continuing to spread southward into the United States. These organisms attach themselves to the inner surfaces of large diameter fresh water inlet pipes for facilities such as power stations, water treatment plants, etc., and quickly reproduce to such an extent that water flow through the pipes is impeded, thereby adversely affecting the facility's operation. This usually requires shutdown of the facility so that measures can be taken to remove the mussels from the pipes.
Various techniques have been proposed to cope with this problem which either prevent the attachment and growth of the mussels in the first place, or provide a mechanical removal process. The prevention techniques include the use of chemicals, such as chlorine, or the use of heat treatment in which hot water is caused to flow through the pipes periodically. The use of chemicals, although effective, is not permitted in most instances because of Environmental Protection Agency regulations, while the use of hot water treatment requires the installation of additional equipment which may be too costly.
Various mussel cleaning and removal techniques have also been proposed and include the use of human divers and mechanical "pigs" which are simple water pressure driven scrapers that work themselves along the lengths of the pipes. Divers are currently the most commonly employed means for scraping mussels from pipe walls, but this is unsafe, prohibitively expensive and requires pipe shutdown. Mechanical pigs or robots have been used with success in mildly obstructed pipes where access to the inlet is not difficult and where pipes can be shutdown for prolonged periods of time. If the pipes are excessively clogged, however, the pigs have a tendency to get stuck in them. In addition, most facilities in the United States do not have redundant pipelines and the shutdown of the pipes for prolonged periods of time is therefore prohibited. Further, access to the pipes is often made difficult because of sharp bends or corners and other protrusions which get in the way of the pigs and prevent them from advancing through the pipes.
Another method for removing the mussels once they have infested an intake pipe employs the use of redundant intake pipes. When the main intake pipe becomes clogged by the mussels, the water flow is diverted through the redundant pipe so that the mussels in the main intake pipe will suffocate. Water flow through the main intake pipe is then resumed and the dead mussels are washed through the pipe since they no longer readily adhere to the pipe's interior wall. The main drawback to this method is again, that it is too costly since it requires installation of a second separate intake pipe system for facility.
In view of the drawbacks of the above known techniques for preventing or eliminating zebra mussel colonization in intake pipes, what is needed then is a new technique which avoids these drawbacks.